These tethered tungsten-alkylidenes serve as catalysts for the synthesis of cyclic polymers. Cyclic polymers can improve the performance and lifetime of products made from synthetic polymers. The worldwide market for Cyclic Olefin Polymers is expected to reach $1,690 million by 2024. A significant challenge in modern polymer chemistry is the efficient and controlled synthesis of polymers with unique topology. Cyclic polymers have a ring-like topology and, therefore, have no chain ends, unlike their linear counterparts. Because of their topology, cyclic polymers exhibit unique physical and chemical properties in both bulk and solution, such as smaller hydrodynamic volume and radius of gyration, higher glass transition temperature, increased rate of crystallization, and so on. Despite the benefits inherent in cyclic polymers, most commercially available polymers have a linear topology, and the synthesis of cyclic polymers is somewhat limited to research laboratories.
Production of stereoregular, cyclic versions of linear polycyclic alkenes have many potential applications. Producing derivatives like cyclic polynorbornene on a large scale is now synthetically possible, but controlling the specific 3D atomic arrangements remains a crucial challenge. Imparting this stereoregularity is critical to manipulating the polymer’s bulk properties. Researchers at the University of Florida have developed tethered tungsten-alkylidenes as catalysts for the synthesis of cyclic polymers. These catalysts facilitate the efficient production of unique and highly stereoregular ring-shaped polymers, like cis-syndiotactic cyclic polynorbornene.
Catalyst for producing cyclic polymers with very high stereoselectivity
Cyclic polymers have unique physical and chemical properties both in bulk and solution-state compared to their linear counterparts. The differences in the properties may lead to the production of new polymer products. The reaction between tungsten alkylidyne and isocyanate occurs to generate tethered tetraanionic tungsten-imido alkylidene complexes, which polymerize norbornene into cis-syndiotactic cyclic polynorbornene via ring expansion metathesis polymerization. The high stereoregularity provides a more rigid and ordered crystalline structure for the generated polymer, while the cyclic topology provides a higher glass transition temperature. That means more heat is required to change the cyclic polymer into a soft, rubbery state; thus, the constructed cyclic polynorbornene retains greater structural integrity in heated conditions than its linear congeners.